SCL - The Neruda lounge is the best in the airport, and one of the better "non-luxury" (ie, without a chef, haircuts, etc.) lounges anywhere.
The Mistral lounge is a pay-per-use lounge available to anyone, run by LA - I do not know for sure, but it may be where the UA RCC was.
You can skip the AA lounge - it was so so.
EZE - The AA lounge is ok. It is not exceptional, but it is pleasant. Further, the gate area is so unappealing, in comparison, the lounge is just, well, great.